Simulating the Novel Phase Separation of a Rapid Proton Capture Ash Composition

TL;DR

This paper uses molecular dynamics simulations to study phase separation in neutron star oceans, confirming previous predictions and validating a computationally efficient method for diverse astrophysical conditions.

Contribution

It demonstrates the effectiveness of a simplified computational method for phase separation, aligning with detailed molecular dynamics results in neutron star ocean compositions.

Findings

Good agreement with previous phase separation predictions

Supports the use of a computationally efficient alternative method

Validates phase separation behavior across different conditions

Abstract

Nucleosynthesis in the oceans of accreting neutron stars can produce novel mixtures of nuclides, whose composition is dependent on the exact astrophysical conditions. Many simulations have now been done to determine the nucleosynthesis products in the ocean, but the phase separation at the base of the ocean, which determines the composition of the crust, has not been as well studied. In this work, we simulate the phase separation of a composition, which was predicted to produce a crust enriched in light nuclei, in contrast with past work which predicts that crust is enriched in heavy nuclei. We perform molecular dynamics simulations of the phase separation of this mixture using the methods of Horowitz $\textit{et. al.}$ (2007). We find good agreement with the predictions of Mckinven $\textit{et al.}$ (2016) for the phase separation of this mixture. Moreover, this supports their method as a computationally efficient alternative to molecular dynamics for calculating phase separation for a wider regime of astrophysical conditions.